To try to answer the original question: the source (CD player, SB, turntable) outputs some voltage signal. The ideal behavior for an amplifier is to boost that signal by some specified factor without distorting it. There are several things which can go wrong with that (I'm going to simplify a bit here for clarity).
One is if you have several sources with different output voltage levels. In that case the amp might not be able to produce the same level of sound from those sources, as it won't be able to boost a smaller voltage as much as a larger. This is an issue mainly with turntables, so if you don't have one you can probably forget about that. If you do, you'll probably need a preamp designed to handle it. Another issue is impedance. When we talk about the voltage output of the source, we mean the result we would get if we put an infinite resistor across the output terminals and measured the voltage across it. Now suppose instead of an infinite resistor, we put a resistor with a finite resistnace across the outputs. Then some current would flow, and because the source isn't perfect the voltage across the resistor would be lower than in the ideal case. When you connect an amp or pre-amp to the source, that infinite resistance is replaced by some finite impedance (which is called the input impedance of that amp or pre-amp). If the input impedance is too low, the source will be trying to output more current than it can handle, and the voltage will decrease. Since impedance is a function of frequency, the voltage will drop more for some frequencies than others, which causes distortion. To avoid that you need a high input inmpedance device connected to the source. Some power amps have high enough input impedance for a given source, but some don't, and in that case an active preamp can help. However if the amp by itself was fine, adding the preamp is simply adding an unnecessary extra component, which will add some (probably minor) level of noise and distortion to the circuit. So in that case the best preamp is a piece of wire. -- opaqueice ------------------------------------------------------------------------ opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=30852 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
